1. Field of the Invention
The present invention relates to a motor used by electrical equipment, and a method for manufacturing the motor, and particularly an a motor suitable for an electrical equipment for vehicles or acoustical equipment, and a method for manufacturing the motor.
2. Description of the Related Art
Generally, a bottomed cylindrical yoke which is formed by deep drawing of a metal plate (i.e., a yoke which holds a magnet at an inner side thereof to form a magnetic circuit) is applied to a small-sized motor used by electrical equipment for vehicles, acoustic equipment, and the like.
However, in the deep drawing process, it is difficult for the wall thickness of an outer peripheral portion of the yoke to be made uniform, and therefore, it is difficult to obtain a satisfactory magnetic circuit. A yoke manufacturing method for solving the above drawback is disclosed in Japanese Utility Model Application Laid-Open (JP-U) No. 57-139252.
In this method, a yoke is formed in such a manner that a base plate is cut out by punching from a metal plate, the formed base plate is then rounded substantially circular in cross section, and facing peripheral end portions of the base plate are connected to each other so as to allow formation of a cylindrical body. End caps are fitted into axial-direction end portions of the cylindrical body. In addition, it is also mentioned that a yoke is formed in such a manner that two base plates which are each rounded substantially in a semicircle in a cross section are caused to face each other, and the peripheral end portions of one of the base plates are connected to peripheral end portions of another base plate, respectively, to form a cylindrical body, and end caps are fitted into axial-direction end portions of the cylindrical body.
On the other hand, in the above-described yoke, a through hole is formed in one of the end caps fitted into the both end portions of the yoke in the axial direction and a motor rotating shaft passes through the through hole.
However, with the above-described yoke structure, the yoke and the end caps are formed separately, and therefore, there is a possibility that the shaft core of the yoke and the center of the through hole of the end cap are positioned apart from each other due to errors of assembling.